A conventional film used for an overhead projector (OHP) application is generally prepared by cutting a roll-type film into a film sheet having a predetermined size, printing or copying a desired image on one surface of the film sheet, and, if necessary, further cutting the film sheet having the printed image.
Such a film used for printing and copying is required to have satisfactory characteristics in terms of toner adhesion property (printing property); antistatic property for suppressing copy degradation during continuous copying, which might occur due to static charge buildup on the surface of the film substrate; friction coefficient and anti-blocking properties to prevent during continuous copying jamming or simultaneous transfer of multiple overlapping films; and runnability to allow high speed-copying without causing jamming or the generation of scratches. In particular, good runnability needed for high speed-copying is critical in increasing the productivity of OHP films.
Therefore, most films developed hitherto for printing and copying are generally composed of a toner receiving binder, an antistatic agent, a slipping agent, and a catalyst (U.S. Pat. Nos. 3,854,942, 4,071,362, 4,415,626, 4,489,122 and 5,310,591), but the above components tend to cause blocking among films, making it difficult to achieve smooth continuous copying. In addition, in order to improve the runnability property of a film, a filler which is capable of making the film surface roughness at a desired level is added during a film manufacturing process. However, the use of a filler usually causes lowering of the optical characteristics of the film, e.g., poor haze. Thus, the use of a filler in an amount suitable for meeting required haze standard leads to an unsatisfactory surface roughness.
Accordingly, for the purpose of achieving smooth transfer of films during printing and copying, a piece of paper is added to one surface of each film to be transferred in a tipped or paperback form, instead of the untipped or bareback form. However, such use of paper creates the problems of high cost and the need for waste treatment after use.